Surgically implanted systems, such as fixation devices and apparatuses, are commonly used to correct a variety of back structure problems, including those that occur as a result of trauma or improper development during growth. A typical spinal fixation system generally comprises a support rod or system of support rods that are secured along at least a portion of the spine by bone screws or hooks or other bone engaging components. Such bone screws may be directly connected to the support rods or may be connected indirectly by using medial/lateral connectors or other similar components. The bone screws, bone hooks, medial/lateral connectors, and related items that function to anchor the support rods to the bones are often collectively referred to as bone engaging hardware or implants.
In a basic spinal fixation system, bone screws have a rod receiving opening extending through a head portion of each bone screw. The bone screws are secured in the vertebra at desired locations and a support rod is then extended through the opening in each bone screw. In order in order to fix the translational and rotational relationship of a support rod within the openings, set screws or caps are typically connected to the screw head as being threaded onto the screwhead or within a bore thereof and are tightened against the support rod. If needed, the support rod is bent or formed to support the spine in a desired manner or to exert the desired corrective or stabilizing forces to the spine. Such support rods may be pre-bent or bent during the procedure. For a spinal alignment correction with such systems, the shape of the support rods are utilized as the means for defining and maintaining the desired spinal curvature or vertebral alignment.
Other fixation systems have been developed that use medial/lateral connectors in association with bone screws to secure the support rods to the vertebra. The bone screws used in these systems typically include a threaded stud extending from the screw heads. The medial/lateral connectors include an arm and a head, and a rod receiving opening that extends through the head for connection to a support rod with a set screw or other locking device. The arm of the connector includes an opening, such as a hole or slot that can receive the threaded stud of a bone screw. A fastener can then be used to attach the bone screw to the medial/lateral connector. This type of system is utilized in correcting spinal structural deformities or abnormalities is the same general manner as the fixation system above described wherein the support rods are shaped to define and maintain a desired spinal alignment.
The fixation systems described above are commonly utilized for defining and maintaining a desired spinal structural alignment, but are not used for creating a motive force to move or shift one vertebra relative to another. Such force creation is typically performed as a distinct procedure. The motive force can be provided manually, such as by the surgeon physically manipulating a vertebra to permit connection of an implant within a vertebra to a pre-bent support rod, or by other drive device utilization, with the purpose of any such manipulation or utilization being to cause some sort of movement or shifting of one or more vertebra to create a desired spinal structural alignment.
The shifting of one or more vertebra for the purpose of at least partially correcting a spinal structural deformity or abnormality, whether as a result of injury, trauma, or a congenital condition, is often referred to as a reduction process or technique. A reduction is any movement toward any healthy, normal, or efficient position as may be determined for any patient. Certain deviations or pathologies from such normal positions are characterized according to the relative directional shifting between adjacent vertebra. Pathologies include, among other things, spondylolisthesis (a front to back misalignment of a vertebral body on another or the sacrum) and, scoliosis (a lateral misalignment of a vertebral body on another of the sacrum).
Reduction techniques include manual methods, where a surgeon provides the requisite force to a vertebra which may include the use of a tool, and device methods, where such a force is generated, compounded, or converted in one way or another for application to a vertebra.
In one type of manual procedure, a spinal fixation system such as described above is used within a reduction process of a vertebra. By such a reduction process, a vertebra is reduced to a more normal anatomical position or other desired position relative to adjacent vertebra and held in place by the implant system. Usually, one or more bone screws are implanted in a vertebra adjacent to a vertebra to be reduced. A shaped support rod is then attached to the bone screw such as may include a medial/lateral connector so that the rod cantilevers over the vertebra to be reduced or bridges a vertebra to be reduced. This process can be repeated so that rods are implanted on opposite sides of a vertebra to be reduced. Next, a bone screw is implanted in the vertebra for connection to the support rod positioned away from the bone screw. Typically, the rod is pre-shaped to position the bone screw connector or medial/lateral connector in a position that will locate the vertebra to be reduced in a desired position. However, the vertebra must be moved or translated so that the bone screw implanted in the vertebra can be attached to the medial/lateral connector such as by manual movement by the surgeon with or without use of a tool.
Devices and methods have also been developed for translating a vertebra relative to another where a force for causing such movement is generated, compounded, or converted by the device for application of the force to one or more vertebra. Typically, a drive force may be provided by a surgeon, which force operates the device mechanism for creating a force to translate a vertebra. Such devices are known to grab a vertebra by way of a hook or screw that may be implanted. Generally, these devices grasp a vertebral portion or an implanted bone engaging element and pull it toward a fixed element either of the device or other support system. Devices have been developed recently that utilize hooks or implants of a spinal fixation system as a bone engaging element for grasping a vertebra and to move it relative to a support rod of the spinal fixation system. See U.S. Pat. No. 5,219,349 to Krag et al, U.S. Pat. No. 5,562,662 to Brumfield et al, U.S. Pat. No. 5,782,831 to Sherman et al, U.S. Pat. No. 5,910,141 to Morrison et al, U.S. Pat. No. 6,248,107 to Foley et al, and U.S. Pat. No. 6,440,133 to Beale et al. Although these devices can be effective for translating such a bone engaging element, they are generally complex and cumbersome to use, especially in the confined spaces available for these types of spinal surgeries. Moreover, these devices require distinct techniques for attaching a bone engaging element to a component of a spinal fixation system and for moving the bone engaging element into a desired position.